Construction materials must be installed correctly to insure the best performance. Wood-based panel products undergo dimensional changes when exposed to elevated moisture conditions. Most panels are put into service conditions at less than equilibrium moisture content. Consequently, there can be an uptake in moisture from the surrounding environment and “growth” in panel dimensions. The term used to describe this phenomenon is linear expansion (LE), whereby physical dimensions (length and width) will grow with moisture uptake.
There are a number of consequences to linear expansion when panels 1 are fitted tightly together at joints 3 prior to expansion (see, e.g., prior art FIGS. 1-3):
1) Panels 1 will buckle 4 somewhere along an unsupported span (FIG. 1).
2) Excessive deflection 5 may result (FIG. 2) in putting surfaces out of level.
3) The upper 8 and lower 9 surfaces (top and bottom faces) of the panel 1 will flare out 7 at the panel-to-panel joint 3 in a release of forces (FIG. 3). This flaring 7 of panel edges at joints 3 is sometimes attributed wholly to edges well, where the uptake of moisture causes expansion in the vertical direction, but is more likely to be a result of a combination of expansion in both directions. Flare-out 7 occurring prior to finishing the structure can necessitate sanding, adding additional cost to construction. Occurrence of edge flaring 7 after finishing can cause gypsum board (drywall) to crack, exterior siding to bulge out, floors or shingles to bulge out, etc.4) Expansion of panels may push walls out of plumb; and5) expansion of a wall system can push floors, ceilings, and roofs off level. In current panel construction, if enough LE occurs and the panel edges come into contact with each other, the compressive force on the surface flakes causes them to raise or “tent” up, causing ridging in the panel joint. This can cause shingles to telegraph the ridging, and can be a cause for customer complaint.
Given that the above expansion characteristics and consequent impacts are well known, most manufacturers, their third-party certification agencies, and governing standards prescribe a minimum gap at panel joints to allow for linear expansion. The amount of gap recommended is dependent on the inherent linear expansion character of the substrate (i.e., some panels will expand more than others).
The American Engineered Wood Association (APA) defines the panel spacing as the gap left between installed structural panels in floor, wall, or roof deck construction (http://wooduniversity.org/glossary.cfm, APA, 2006) and indicates that spacing distance should be enough to allow for any possible expansion due to changing moisture absorption levels to help prevent buckling and warping.
In general, when wood-based sheathing panels are installed, a ⅛″ space between adjacent panel edges is recommended. Common techniques for spacing panels are simply to measure the gaps formed between deck boards as they are installed or to drive 8d or 10d nails into joints next to an installed deck board and place the next deck board against the nails. Previous methods for spacing include:
1) 8d or 10d box nails for gauging ⅛″ spacing between panels or other spacers;
2) H-clip with spacing distance between adjacent panels (mechanical attachments); and
3) Panel edge profiling using a tongue and groove (T&G). A minimum ⅛″ gap between square edged panels is recommended when the panels are applied to framing members. Often, the framers or roofers are not aware of the recommended ⅛″ spacing for structural wall panels, and certainly, this is not common practice in the field. Some framers even believe that leaving the recommended space is a code violation. It is believed that excessive education and training are required regarding the need for ⅛″ spacing if not using existing mechanical spacers such as H-clips or nails.
Most warranty claims and problems of the above nature presented to panel manufacturers arise from improper installation—the panels were not gapped as prescribed. Whether due to inexperienced installers, insufficient gapping from imprecise measurement tools, or time constraints in building schedules, proper gapping is not being done on all product installations.
Thus, problems associated with wood-based panels being installed without proper spacing has persisted for many years without solution. Consequently, a self spacing panel will be highly desirable for saving installation time and increasing value since the need for a separately installed spacer can be eliminated in the processes.